Well, at some point Japan will have (and already has) a lot of people with Korean roots, what would mean that minorities will be rather present even +1000 years. I mean, sure, they will change, but for some reason we have revived Latin (it is a living language right now!), because there are no Romans, yet the language is used. I mean, lacking of country does not mean there's no such nationality (finest example: Poland with 123 years without own country). However strong would you try, nationalities (or its rather now ethicity in Freelancer) will be present, because there will be people maintaining traditions of usage of the other languages.
I mean, there are still Native South Americans, even right now, who speak in Spanish and in their own languages, because they were firstly killed by Spaniards, but later then they were taken into Great Spanish Empire. Not to mention while we speak about "Chinese" we mean either Mandarin or Cantonese, forgetting that China is place of over 30 Chinese languages (or dialects - linguists are still arguing about how the hell class that s**t).
Not to mention Tibetan language (but this fact is kinda wrong, because Tibet is a part of China for mere 70 years, yet in 7th C. Tibet was so annoyed with China that they did a blitzkrieg straight to their capital).
Yet the finest example about the language itself is Gaelic, which was "ressurected" by Irish in both Northern Ireland and Republic of Ireland - I was there during vacations and if not English, I would be WAY CONFUSED about the names.